1. Field of the Invention
The invention pertains to a device for coupling an asynchronous motor with an electrical power cable. More specifically, the invention pertains to a coupling device for making an asynchronous motor work in a star connection or delta connection depending on a user's needs. The invention also pertains to an asynchronous motor of this kind provided with a coupling device of this kind. Similarly, the invention pertains to a method for coupling an asynchronous motor with an electrical power cable using a coupling device of this kind.
An asynchronous motor is an alternating current electrical machine comprising a stator, linked to a speed variator, and a rotor crossed by currents induced by the magnetic field created by the stator currents. An asynchronous motor is generally connected to a three-phase network. A three-phase asynchronous motor of this kind can be driven in a star coupling configuration or in a delta coupling configuration. Depending on the use, or final purpose, of the asynchronous motor, it may be worthwhile to have a three-phase asynchronous motor in a star coupling or a three-phase asynchronous motor in a delta coupling.
As can be seen in FIGS. 1A and 1B, the three coils A, B and C of the rotor of an asynchronous motor are each connected to two wires of the electrical output of the asynchronous motor, which have six of them in all. Furthermore, each coil is connected to one of the three wires L1, L2 and L3 of the power supply cable. The coils A, B, C can thus be mounted in two ways, either in a star configuration (FIG. 1A) or in a delta configuration (FIG. 1B).
The choice of the wiring of the asynchronous motor is generally done when it is being mounted in the final device that must receive it, and as a function of the characteristics sought. For example, when it is desired to reduce the intensity of the motor at start-up, there are known ways of using a star-coupled three-phase asynchronous motor (FIG. 1A). Conversely, when it is desired to exploit the maximum power torque of the asynchronous motor, there are known ways of using a delta coupling (FIG. 1B).
The star coupling of FIG. 1A is generally obtained by having two connection strips 12, 13 as shown in FIG. 1B. These connection strips 12 and 13 put the terminals X, Y and Z at the same neutral potential. The terminals U, V and W can then be wired with the three conductors L1, L2 and L3.
Conversely, as can be seen in FIGS. 2A and 2B, the delta coupling is obtained by using three connection strips 14, 15 and 16 each connected independently of the others to two terminals, respectively Z and U, V and X, W and Y in FIG. 2B. The three conductors L1, L2 and L3 of the power supply cable are then each connected to a connection strip 14, 15 and 16.
A choice of the operating mode such as this is generally done at the outset and generally not modified thereafter.
2. Description of the Related Art
FIG. 7 shows an example of a prior-art asynchronous motor 1 provided with an open terminal box or junction box 2. In the internal volume 5 of the junction box 2 are housed the six terminals U, V, W, X, Y, Z, or coils of the rotor. The three wires of the power supply cable 4 open out into the junction box 2 through a via hole 3 made on the wall of the junction box 2. Each wire (not shown) of the power cable 4 is wired individually to a terminal U, V, W, X, Y, Z of the rotor. Two connection strips 12, 13 enable a star-shaped coupling as shown in FIG. 1B, each strip 12, 13 being fixed individually between two terminals X and Z, and X and Y respectively.
Thus, when an installer wishes to install an asynchronous motor 1 of this kind with a given mode of operation, he must bring the power cable 4 through the hole 3 so that the three wires of the power cable 4 open out into the internal volume 5 of the junction box 2. He then fixes the connection strips 12, 13 between the terminals X, Y and Z to obtain the star-shaped wiring. The installer must then individually connect the three wires of the power cable 4 to the remaining terminals U, V and W. Then he puts back the lid (not shown) on the junction box 2 and fixes it by means of four screws. Thus, the connection, the choice of the mode of operation and the implementation of the corresponding coupling are painstaking operations since it is necessary to work terminal by terminal and wire by wire, and moreover, the installer has to open up and then re-shut the junction box 2.